1. Field of the Invention
The present invention relates generally to the production of bent glass sheets, and more particularly to an improved method of and apparatus for supporting and deforming the glass sheets in a press bending operation.
2. Description of the Prior Art
In accordance with one system for mass producing curved or bent glass sheets such as glazing closures for automobiles or the like, the sheets are supported and advanced along a generally horizontal path on the driven rolls of roll-type conveyors successively through heating area and bending areas, and then through a heat treating area for appropriate thermal treatment to anneal or temper the bent sheets as may be desired.
Upon emerging from the heating furnace the heated sheets advance into the bending area and are precisely positioned therein between complemental upper and lower shaping members by retractable locating stops positioned in the path of movement of the advancing sheets so as to engage the leading edges thereof and stop the sheets at the appropriate position. The lower press member is then raised so as to engage the properly oriented sheet around its marginal edge portions and lift the sheet from the conveyor rolls for pressing between the complementary shaping surfaces of the press members to the predetermined desired curvature.
While the sheet is in the highly heated, softened condition necessary for proper bending, it is susceptible to damage which may result in optical defects unacceptable, or at least undesirable, in the finished glazing unit. One such defect is that commonly known as "roll distortion", caused by marring of the sheet surface due to relative frictional movement between the glass surfaces and the rotating conveyor rolls, particularly when the advancing movement of the sheet is interrupted by the locating stops while the conveyor rolls continue to rotate momentarily. This problem is addressed in U.S. Pat. No. 3,905,794. In accordance with the patent, relative movement between the contacting surfaces of the glass sheet and the conveyor rolls is eliminated by providing in the bending area a series of conveyor rolls of generally arcuate form, rotatable about their own axes and also pivotable between a first planar position for supporting a glass sheet prior to the bending thereof, and a second position extending at an angle to the horizontal plane of the first position so as to be out of engagement with the sheet prior to bending and yet supporting a bent sheet of glass while maintaining the desired curvature imparted thereto. Each of the conveyor rolls comprises a non-rotating inner core member and an outer sleeve mounted for rotation about and relative to the inner core member. In order to support the heated sheet throughout its length both before and after it is bent, the conveyor rolls are mounted at their ends outwardly of the press member.
The lower or female press member is generally of ring-type construction having a shaping rail which engages only the peripheral margin of the sheets. In order to permit the shaping rail of the lower press member to be moved vertically between its lowered position beneath the conveyor rolls and its raised position thereabove, the shaping rail is comprised of a plurality of individual segments arranged in spaced, end-to-end relationship in the desired outline pattern. The adjacent ends of the segments are suitably spaced to permit the rolls to pass therebetween. The shaping rails are generally of substantially rectangular configuration in plan so that the two end sections thereof extend substantially normal to the axes of the rolls. Even though the spaces or gaps between adjacent shaping rail segments may thus be minimized, the heat softened glass sheet is unsupported in these spaces as it is lifted by the lower press member so that sagging and marking of the glass may occur. The individual segments must be precisely aligned or they may cause undue marking of the sheet, and thus the segmented shaping rail is more difficult and expensive to fabricate and use than a comparable continuous shaping rail.
More recent automotive styling has dictated the fabrication of more complex and elaborate glass shapes, some of whose outlines require shaping rails having portions intersecting the rolls at acute angles so that the spacing between adjacent shaping rail segments must be significantly increased. This, of course, greatly increases the likelihood of sagging in the spaces between segments. In an effort to avoid this problem, U.S. Pat. No. 4,116,662 employs conveyor rolls formed of two sections whose outer ends have a common axis and whose inner ends are axially offset from each other and are interconnected by an irregularly shaped member. The gap in the shaping rail can thus be minimized so as to accomodate only the interconnecting member, or eliminated entirely by use of a suitably complexly shaped interconnecting member. In either event there is a resulting gap in the supporting surfaces of the conveyor rolls at the interconnected inner ends thereof. Thus, while improved devices have been proposed for bending glass sheets with reduced distortion resulting from marring of the surfaces due to relative frictional movement between the glass surfaces and rolls, as well as from sagging of the heat softened glass in the spaces between adjacent segments of the shaping rail, there remains a need for a press bending apparatus which is not complex and wherein there is provided improved support for the heated glass sheets both during the conveying and the press bending thereof.